1. Field of the Invention
The present invention relates to a static air-bearing which provides a gas layer between two relatively movable parts (fixed part and movable part) and a predetermined clearance between the two parts, to a stage apparatus using the air-bearing, and to an optical apparatus using the state apparatus.
2. Description of the Related Art
In the process for producing semiconductor devices, to project a circuitry pattern onto a wafer, a mask or reticle (hereinafter "reticle") forming the circuitry pattern to be projected thereon is used. During the process to manufacture the intended semiconductor wafer, an inspection apparatus is used to inspect whether the circuitry pattern to be projected has been accurately formed on the wafer in accordance with a circuitry design.
The inspection apparatus is designed to be able to inspect the whole surface of the wafer to be inspected by moving the wafer using a stage apparatus. A static air-bearing is used in the stage apparatus accommodated in the inspection apparatus, because high positioning accuracy is required.
Referring to FIG. 10, such stage apparatus using a static air-bearing will be explained. FIG. 10 is a sectional view of a stage apparatus. In FIG. 10, an X-axis and a Y-axis, perpendicular to each other, are set in a plane parallel to a installation floor G; and, a Z-axis is set perpendicular to the installation floor G.
This stage apparatus has a stage 102 which mounts a wafer 101 to be inspected on it. The stage 102 is connected to a movable part 103 of a static air-bearing (103, 104). The movable part 103 has a rectangular sectional profile. A fixed part 104 is disposed so that the three surfaces of the -X side end portion of the movable part 103 and of the +X side end portion of the movable part 103 are surrounded by this fixed part 104. Further, the fixed part 104 is fixed on the installation floor G via a fixing part 105.
Bearing pads 104a which blows air from a air supply (not shown) into the space between the fixed part 104 and the movable part 103, are disposed at each surface of the fixed part 104 facing the movable part 103. Further, air exhaust grooves 104b which temporarily store the air blown out of the bearing pads 104a are formed around the bearing pads 104a to exhaust the air; and, air exhaust ports 104c which are connected to a vacuum pump (not shown) are provided with the air exhaust grooves 104b.
In the static air-bearing (103, 104), the air is continuously blown into the space between the movable part 103 and the fixed part 104, and the blown up air is temporarily stored in the air exhaust grooves 104b and then exhausted through the air exhaust ports 104c. Therefore, an air layer of approximately constant pressure is formed in the space between the movable part 103 and the fixed part 104, and the movable part 103 and the fixed part 104 will be kept apart at a predetermined clearance.
A movable piece 106 of a linear motor (106, 107) is connected to the movable part 103, and the movable piece 106 is disposed so that the movable piece 106 faces a stator 107 leaving a space. The linear motor (106, 107) can move the movable piece 106 in the Y-direction along the stator 107.
Referring now further to FIG. 11A, the static air-bearing of the stage apparatus will be explained. FIG. 11A is a sectional view of the movable part 103 and the fixed part 104, illustrated in FIG. 10, taken on line A--A in FIG. 10, and is attached with a similar coordinate system.
In this static air-bearing, the length of the movable part 103 must be longer than the length of the fixed part 104 by approximately the moving stroke, because the bearing pads 104a on the fixed part 104 and movable part 103 need to face each other during the movement of the movable part 103. The movable part 103 moves up to the position indicated by the dashed lines in the Figure.
Thus, relative to this static air-bearing, approximately two times the length of the moving stroke over the fixed part 104 is to be secured to satisfy the free movement of the movable part 103 with respect to the Y-direction, which yields a problem that this bearing becomes large sized.
Accordingly, another problem that a stage apparatus which uses this static air-bearing also becomes large sized arises. Also, an inspection device which accommodates this stage apparatus become large sized. Those problems also occur, not only with respect to the inspection device, but also with respect to other optical apparatuses which accommodate similar stage apparatuses, e.g., exposure apparatuses that are used in the lithography process for producing semiconductor or LCD elements, electron microscopes, or electron beam apparatuses that transfer or form circuitry patterns on substrates by irradiating electron beams onto substrates.
By contrast, in such static air-bearing as shown in FIG. 11B in which bearing pads and air exhaust ports are disposed on a movable part, the movable part needs only to move up to the position indicated by the dashed lines in the FIG. 11B while this air-bearing is configured to realize a similar moving stroke as is realized by the air-bearing shown in the above FIG. 11A. Thus, the adoption of this air-bearing makes the length to be secured with respect to the Y-direction shorter.
However, in the static air-bearing disposing the bearing pads and the air exhaustion ports on the movable part as shown in FIG. 11B, a problem that arrangement of pipes relayed to the air exhaustion ports becomes very difficult arises. That is, the pipes for air exhaustion are generally made of metallic, elastic bellows so that the pipes do not crush due to sucking force caused by air suction by means of a vacuum pump and still follow the movement of the movable part. While a certain force is necessary to give the metallic bellows telescopic motion, it is difficult to give the metallic bellows smooth telescopic motion following the movement of the movable part.
For example, in the configuration in which force being executed on the movable part also gives the bellows the telescopic motion, reaction force from the bellows executes on the movable part, so that a proper clearance between the fixed part and the movable part might not be maintained or accurate movement of the movable part might be influenced.
An object of the present invention is to provide a static air-bearing which can limit its size and can make pipe arrangement easy, a stage apparatus using the air-bearing, and an optical apparatus using the stage apparatus.